The present invention relates to medical devices, and more particularly to stenting and treatment of bifurcated vessels. A stent is an implantable scaffold that is typically delivered percutaneously and deployed in a vein, artery, or other tubular body organ for treating an occlusion, stenosis, aneurysm, collapse, dissection, or weakened, diseased, or abnormally dilated vessel or vessel wall. The stent is radially expanded in situ, thereby expanding and/or supporting the vessel wall or body organ wall. In particular, stents are quite commonly implanted in the coronary, cardiac, pulmonary, neurovascular, peripheral vascular, renal, gastrointestinal and reproductive systems, and have been successfully implanted in the urinary tract, the bile duct, the esophagus, the tracheo-bronchial tree and the brain, to reinforce these body organs.
Stents are often used for improving angioplasty results by preventing elastic recoil and remodeling of the vessel wall and for treating dissections in blood vessel walls caused by balloon angioplasty of coronary arteries, as well as peripheral arteries, by pressing together the intimal flaps in the lumen at the site of the dissection. Conventional stents have been used for treating more complex vascular problems, such as lesions at or near bifurcation points in the vascular system, where a secondary artery branches out of a typically larger, main artery, with limited success rates.
Conventional stent technology is relatively well developed. Conventional stent designs typically feature a straight tubular, single type cellular structure, configuration, or pattern that is repetitive through translation along the longitudinal axis. In many stent designs, the repeating structure, configuration, or pattern has strut and connecting balloon catheter portions that can impede blood flow at vessel bifurcations.
Furthermore, the configuration of struts and connecting balloon catheter portions may obstruct the use of post-operative devices to treat a daughter vessel in the region of a vessel bifurcation. For example, deployment of a first stent in the mother lumen may prevent a physician from inserting a daughter stent through the ostium of a daughter vessel of a vessel bifurcation in cases where treatment of the mother vessel is suboptimal because of displaced diseased tissue (for example, due to plaque shifting or “snow plowing”), occlusion, vessel spasm, dissection with or without intimal flaps, thrombosis, embolism, and/or other vascular diseases. A regular stent is designed in view of conflicting considerations of coverage versus access. For example, to promote coverage, the cell structure size of the stent may be minimized for optimally supporting a vessel wall, thereby preventing or reducing tissue prolapse. To promote access, the cell size may be maximized for providing accessibility of blood flow and of a potentially future implanted daughter stent to daughter vessels, thereby preventing “stent jailing,” and minimizing the amount of implanted material. Regular stent design has typically compromised one consideration for the other in an attempt to address both. Problems the present inventors observed involving daughter jailing, fear of plaque shifting, total occlusion, and difficulty of the procedure are continuing to drive the present inventors' into the development of novel, delivery systems, which are easier, safer, and more reliable to use for treating the above-indicated variety of vascular disorders. Although conventional stents are routinely used in clinical procedures, clinical data shows that these stents are not capable of completely preventing in-stent restenosis (ISR) or restenosis caused by intimal hyperplasia. In-stent restenosis is the reoccurrence of the narrowing or blockage of an artery in the area covered by the stent following stent implantation. Patients treated with coronary stents can suffer from in-stent restenosis.
Additionally, alignment of the side branch stent with the main branch stent can be challenging. If the two stents are not properly aligned, the ends of the stent may overlap with one another resulting in metal on top of metal, an undesirable situation. Also, if the two stents are not properly aligned, a gap may exist between the ends of the stent, resulting in an unstented or unscaffolded region in the vessel. Moreover, the unstented region may not receive a drug that is eluted from the stent. Thus, the unstented region may be more likely to experience restenosis. It would therefore be desirable for the side branch stent and the main branch stent to accurately align with one another upon expansion into the bifurcation.
Many pharmacological attempts have been made to reduce the amount of restenosis caused by intimal hyperplasia. Many of these attempts have dealt with the systemic delivery of drugs via oral or intravascular introduction. However, success with the systemic approach has been limited.
Systemic delivery of drugs is inherently limited since it is difficult to achieve constant drug delivery to the afflicted region and since systemically administered drugs often cycle through concentration peaks and valleys, resulting in time periods of toxicity and ineffectiveness. Therefore, to be effective, anti-restenosis drugs should be delivered in a localized manner. One approach for localized drug delivery utilizes stents as delivery vehicles. For example, stents seeded with transfected endothelial cells expressing bacterial betagalactosidase or human tissue-type plasminogen activator were utilized as therapeutic protein delivery vehicles. See, e.g., Dichek, D. A. et al., “Seeding of Intravascular Stents With Genetically Engineered Endothelial Cells,” Circulation, 80:1347-1353 (1989). U.S. Pat. No. 5,679,400, International Patent Publication No. WO 91/12779, entitled “Intraluminal Drug Eluting Prosthesis,” and International Patent Publication No. WO 90/13332, entitled “Stent With Sustained Drug Delivery” disclose stent devices capable of delivering antiplatelet agents, anticoagulant agents, antimigratory agents, antimetabolic agents, and other anti-restenosis drugs. U.S. Pat. Nos. 6,273,913; 6,383,215; 6,258,121; 6,231,600; 5,837,008; 5,824,048; 5,679,400; and 5,609,629 teach stents coated with various pharmaceutical agents such as Rapamycin, 17-beta-estradiol, Taxol and Dexamethasone. This and all other referenced patents are incorporated herein by reference in their entirety. Furthermore, where a definition or use of a term in a reference, which is incorporated by reference herein is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Therefore, given the challenges of current stent technology, a need exists for improved stent delivery systems and methods, particularly for treating bifurcated vessels. At least some of these objectives will be met by the present invention.